Conventionally, as a material used for a solder resist of a printed circuit board, a photocurable resin composition which can be developed with an aqueous alkaline solution is employed. For example, in Patent Documents 1 and 2, a photocurable resin composition which contains an epoxy acrylate-modified resin induced by modification of an epoxy resin (hereinafter, may be simply referred to as “epoxy acrylate”) is used.
One example of a method of forming a solder resist using such a photocurable resin composition is a method in which a photocurable resin composition is coated and dried onto a substrate to form a resin layer and the resulting resin layer is then irradiated with a light in a pattern form and developed with an alkali developer, thereby forming a solder resist.
Meanwhile, Patent Document 3 discloses a composition which has an improved desmear resistance by not containing a thermosetting resin having a secondary hydroxyl group. Using this composition, for example, a solder resist is formed by screen printing.
Further, Patent Document 4 discloses a method of forming a solder resist layer composed of a thermosetting resin composition on one side of a printed circuit board and a solder resist layer composed of a photocurable resin composition on the other side. Patent Document 4 also discloses a method of forming an opening having a relatively small diameter on the solder resist composed of a thermosetting resin composition by laser processing and an opening having a relatively large diameter on the solder resist layer composed of a photocurable resin composition by photolithography.